Dynamics of Suspended Sediment Variability Over Various Timescales: A Quantitative Analysis Using Remote Sensing Data

Suspended sediment concentration (SSC) significantly impacts the water quality and morphodynamics of coastal water bodies. The highly turbid zone coverage (HTZC), i.e., the area covered by high SSC, varies on different timescales in response to dynamic factors. However, quantitative analyses concerning periodic HTZC variation and its response to dynamic forcing remain insufficiently understood. Based on SSC data collected by the Geostationary Ocean Color Imager during 2012–2020, this study quantifies spatio-temporal HTZC variations for coastal and shelf waters of the Jiangsu coast, located in the southern Yellow Sea, China. The 100 mg/L SSC contour’s offshore distance (SCOD) is computed as an index to represent HTZC. The Lomb-Scargle periodogram detects strong seasonal and fortnightly cycles in the SCOD dataset. The phase-folding analysis reveals that the seasonal cycle dominates the HTZC variations and is modulated by significant wave height. Seasonally, the cross-shore expansion of HTZC is 41–65 km. During the fortnightly tidal cycle, the interaction between the two principal semi-diurnal tidal constituents, M₂ and S₂, leads to a periodic change in the tidal range. This fortnightly change causes variations in the HTZC, with the cross-shore expansion fluctuating between 11 and 20 km. Along the Jiangsu coast, the cross-shore expansion range of HTZC increases from the north to the south, suggesting complex 2D sediment dynamics. Moreover, a time lag exists between the HTZC variation and dynamic factors, with an order of 1–2 months and less than one day on seasonal and fortnightly timescales, respectively. Our findings highlight features in SSC variation that are commonly ignored in traditional visual interpretation and the advantage of the proposed methodology in revealing mechanisms for suspended sediment variation.